I. Technical Field
The present invention relates to an endless belt type grinding tool configured to grind an object by rotationally driving an endless grinding belt and pressing the endless grinding belt against the object.
II. Description of the Related Art
FIG. 1 shows a general structure of an endless belt type grinding tool. As shown in the figure, the tool includes a body 12 with a built-in air motor 10, a drive pulley 14 mounted on the body and driven by the motor, a tubular holding portion 16 extending forward from the body 12 in a direction perpendicular to a rotational axis of the drive pulley 14 (in the leftward direction in the figure), a tension bar 18, which is inserted rearward from the front end of the tubular holding portion into the tubular holding portion and extending forward from the front end, an idle pulley 20, which is mounted on the distal end of the tension bar, an endless grinding belt 22, which is wound between the idle pulley and the drive pulley, and a coil spring 24, which is disposed in the tubular holding portion 16 and urging the tension bar 18 forward to the illustrated position to apply tension to the endless grinding belt 22. The tool grinds a workpiece by rotationally driving the endless grinding belt 22 by means of the air motor 10 and pressing the endless grinding belt against the workpiece.
The endless belt type grinding tool also has a locking member 26, which is used when the grinding belt 22 is replaced. The locking member 26 is formed of a rectangular metal sheet bent into an L shape. The locking member 26 includes an inner portion 26-2, which is disposed so as to traverse the tension bar 18 and has an opening 26-1 through which the tension bar passes, and an outer portion 26-3, which is extending perpendicularly from the inner portion so as to be exposed on a surface of the body of the endless belt type grinding tool such that an operator can push the outer portion. The locking member 26 is urged by means of a spring member (not shown) such that the outer portion 26-3 is urged toward the outer side of the body 12 (the lower side in the figure). When the tension bar 18 is pushed from the illustrated position against the coil spring 24 and then an annular groove 18-1 formed on the outer peripheral surface of the tension bar aligns with the opening 26-1 of the locking member, the edge of the opening 26-1 is moved by the spring member so as to engage with the annular groove 18-1, whereby the locking member retains the tension bar against the coil spring 24.
When the grinding belt 22 is replaced, the tension bar 18 is pushed against the coil spring 24 into the tubular holding portion 16 from the state shown in FIG. 1, and then the tension bar is locked by means of the locking member 26. Thus, the distance between the idle pulley and the drive pulley is decreased, whereby the tension of the endless grinding belt is removed. In this state, the endless grinding belt is removed from the pulleys, and then a new endless grinding belt is wound around the pulleys. After that, the outer portion 26-3 of the locking member 26 is pushed in to release the tension bar 18 locked by the locking member 26. Then, the tension bar is pushed forward by means of the coil spring 24 to apply tension to the new endless grinding belt.
An example of such endless belt type grinding tools is disclosed in Japanese Patent No. 3826133.